(1) Field of the Invention
The present invention relates to an improvement in the method for stretching attachment devices for attaching tags and the like to merchandise.
(2) Brief Description of the Prior Art
Various attachment devices for attaching tags and the like to merchandise, which are integrally molded from synthetic resins such as nylon, have heretofore been proposed and developed. The prototype of now broadly used attachment devices was developed by Dennison Manufacturing Company, U.S.A., and the structure is disclosed in the specification of U.S. Pat. No. 3,103,666. More specifically, the attachment device disclosed in this U.S. patent specification comprises a cross-bar, a filament extending from the central portion of the cross-bar rectangularly thereto and a head attached to the filament rectangularly thereto. When this attachment device was first developed, the foregoing three portions were merely molded integrally from a synthetic resin, and the strength of the filament portion was low and it was difficult to secure tags or the like by means of such attachment device.
As is well known in the art, in a linear polymer, just after molding molecules are not arranged in a certain direction and therefore, the strength among molecules is very low. Accordingly, the above-mentioned attachment device is fragile and is readily broken when slightly bent. As means for overcoming this defect, there has been developed and adopted a method in which the filament portion is stretched to cause orientation of molecules and increase the strength.
This method for stretching attachment devices is divided into two types; namely, a method in which an attachment device is taken out of a mold after molding and the attachment device is fed to a stretching machine and is stretched, and a method in which an attachment device is stretched immediately after molding by utilizing a mold. The former method is not suitable for high-speed stretching because the method involves two separate steps and the stretchability is degraded because of moisture absorbed during the course between the two steps. Moreover, this method is defective in that the productivity is low. The latter method is far excellent over the former method with respect to the productivity because the stretching step can be conducted continuously to the molding step.
At the step of the filament portion, it is important that filaments of a group of attachment devices should be uniformly stretched and that cross-bars should not be deformed during the stretching step. However, these two important requirements can hardly be satisfied according to any of the foregoing conventional methods. Therefore, the stretching cannot but be performed at low speeds very carefully, and according to the conventional methods, it is very difficult or impossible to perform the stretching operation at a high speed uniformly.